In CTD operations, a BHA comprising, inter alia, a downhole motor having a drill bit connected thereto is made up to a CT string and drilling takes place by rotating the bit with the downhole motor by pumping drilling fluid through the CT and applying weight to the bit. In this respect, CTD operations are essentially the same as conventional drilling operations with a downhole motor and drill pipe forming the drill string. However, since CT is continuous, it is not necessary for the drilling to be interrupted to add more pipe to lengthen the drill string. In CTD operations the CT drill string is advanced into the well or withdrawn from the well using a CT injector head as is common in CT operations. Consequently, it is unnecessary to have a derrick or mast, draw works and rotary table or top drive to handle or drive the drill string as in conventional rotary drilling.
In drilling operations, the drill string and. BHA can become stuck for a variety of reasons which are generally considered as mechanical sticking or differential sticking. In such cases, the overpull required to free the drill string or BHA is greater than that available from the rig. While certain remedial operations are available, it is often the case that it becomes necessary to back off and to retrieve the stuck tool in a fishing operation. With a conventional pipe drill swing, this is done by locating the stuck point in the drill string with an appropriate wireline tool inside the drill string and then lowering an explosive charge to the level of the pipe joint above the stuck point. This charge is detonated while a torque is applied to the swing to unscrew this joint and allow the free part of the drill string to be withdrawn from the well. CTD operations differ in that there are no pipe joints to disconnect nor is it normally possible to apply torque to the drill swing since there is no rotary drive at the surface. In addition, running in of a wireline tool or explosive cutter would require first cutting the CT at the surface. Sticking is encountered in non-drilling CT operations and it is normally the tools connected to the CT which become stuck. Consequently, the connector often includes a disconnect mechanism which can be actuated by pumping fluid through the CT, often in conjunction with dropping a ball into a ball seat in the connector to block the flow passage and allow sufficient pressures to be generated to operate the disconnect.
Generally it is the BHA which becomes stuck in CTD operations but conventional CT connectors are inappropriate for drilling operations because they involve a threaded connection. While this is acceptable for non-drilling applications where there is no torque on the joint in the connector, it is not suitable for CTD operations since the drilling action causes torque to be applied to the BHA and CT. In conventional drilling operations threaded joints can be tightened to an appropriate torque using the rotary power available at the rig floor, rotating the drill string, the new pipe or both. However, such rotary power is not normally available in CTD operations nor is it normally possible to rotate the drill string. All threaded connections may be made up with power tongs, except the final one where the injector is made up to the BHA preventing the use of power tongs.
The lack of rotary power to apply the torque typically required for conventional threaded joints (often in the order of 2000 ft lbs) and the inability to rotate the CT has been encountered before in CT operations and joints which do not require rotation of the CT or tool have been proposed. These generally involve threaded rotatable collars on one pan of the connector which engage threaded portions on the other pan such that when tightened, the two pans are drawn together. However, such joints are not capable of transmitting drilling torque across the joint but this is not a problem in conventional operations where negligible torque is encountered.
It is an object of the present invention to provide a connector suitable for CTD operations which does not require high levels of torque to make the connection yet which is able to transmit the torque encountered in drilling across the joint.